Cruise control system for automotive vehicle

ABSTRACT

A cruise control system for an automotive vehicle which automatically controls the throttle valve opening to maintain the vehicle speed constant without a driver&#39;s operation of the accelerator pedal once the vehicle speed is set to a desired value, is designed so that acceleration at the time of operating an increase set switch or resume switch is increased to ensure a comfortable drive while ascending a long slope. To this end, the cruise control system is provided with an overdrive controller which releases overdrive at the time of operating the increase set switch and resumes the overdrive at the time of releasing the operation of the increase set switch, or an overdrive controller which releases overdrive at the time of operating the resume switch when the vehicle speed at that time is sufficiently lower than the set speed and resumes the overdrive when the vehicle speed has been restored substantially to the set speed. Further, in the cruise control system which is adapted to prevent a decrease in the vehicle speed during hill climbing by releasing and resuming the overdrive, a timer is provided which is reset when the vehicle speed has been reduced and is set when the vehicle speed has been restored substantially to the set speed. Even if the vehicle speed has been restored to the set speed, resumption of the overdrive is retarded by the set time of the timer.

This is a division, of application Ser. No. 382,413, filed 26 May 1982.Now U.S. Pat. No. 4,463,822.

BACKGROUND OF THE INVENTION

The present invention relates to a cruise control system for anautomotive vehicle, commonly referred to as an auto-drive or speedcontrol, which automatically controls the vehicle speed without adriver's operation of the accelerator pedal once the vehicle speed isset to a desired value.

In general, cruise control systems of this kind are roughly divided intothose employing a motor type actuator which drives an accelerator linkusing a motor as a power source and those utilizing a negative pressuretype actuator which drives the accelerator link using the intakemanifold absolute pressure as a power source. Since the former isdisadvantageous in terms of weight, cost and responsinity, the latter,which is free from such defects, has been chiefly employed in recentyears. An increase set function is also known which allows an increasein the vehicle speed, without a driver's operation of the acceleraterpedal, only by keeping on pressing a switch called an increase setswitch and which permits a constant speed drive thereafter at the speedof when the increase set switch was released. With the conventionalcruise control system employing the aforementioned negative pressuretype actuator, such a function cannot be sufficiently performed becausethe desired acceleration cannot be obtained when the driver desires toincrease the vehicle speed. That is to say, in this kind of system,acceleration is carried out by introducing the intake manifold absolutepressure 100 percent into the actuator during increase, but since theintake manifold absolute pressure rises with an increase in the throttlevalve opening, the actuator generating power gets into equilibrium withthe reaction force of the accelerator link at a midpoint of the fullstroke, making it impossible to develop an acceleration that meets thedriver's requirement.

Another function of the cruise control system is a resume functionwhich, even after releasing a constant speed driving operation byoperating a brake switch or the like, allows the vehicle speed to returnto its originally set speed, without involving an operation of theaccelerator pedal, only by manipulating a switch called a resume switch.With the conventional cruise control system employing the negativepressure type actuator, however, such a function cannot fully befulfilled because the vehicle speed cannot be restored to the set speedwithin a desired period of time. Namely, with the cruise control systemof this type, in the case where the vehicle speed at the time ofoperating the resume switch is more than about 10 Km/h below the setspeed, the intake manifold absolute pressure is introduced 100 percentinto the actuator, but the desired acceleration cannot be developed forthe same reason as mentioned previously; namely, much time is requiredfor restoring the vehicle speed to the set one, thus failing to satisfythe driver's demand for a sporty drive.

Furthermore, in the case of ascending a long slope of, for instance,about five percent, using overdrive, since the vehicle speed graduallylowers even if the throttle valve is opened full, a steady speed driveat a desired speed cannot be accomplished. To prevent the reduction ofthe vehicle speed while ascending a slope, a certain kind of cruisecontrol system is designed so that when the vehicle speed has becomelower than the set speed by a predetermined value, for instance, 7 Km/h,the overdrive is released and the transmission is automatically changedover, for example, from fourth gear to third to restore the vehiclespeed, and so that when the vehicle speed has returned substantially tothe set speed, for instrance, about 3 Km/h below the set speed, theoverdrive is resumed. With such a method, however, the changeover cyclefrom the overdrive to the immediately lower gear of the transmission orvice versa may sometimes become extremely short according to thegradient of the slope, so that the vehicle speed is frequently altered,resulting in a very uncomfortable drive. Since the cruise control systemis primarily intended to reduce the fatigue of long, high-speed driving,factors providing such uncomfortable driving must be eliminated as muchas possible. A solution to this problem is, for example, to release theoverdrive while ascending a slope and to continue driving at theimmediately lower gear. In this case, however, it is technicallydifficult to automatically release the overdrive, while detectingwhether the slope is upward or downward and its gradient; in addition,driving at the immediately lower speed throughout the ascending of theslope consumes fuel, and hence is uneconomical.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a cruisecontrol system which is free from the aforementioned defects of theprior art and hence has improved performance.

Another object of the present invention is to provide a cruise controlsystem employing the negative pressure type actuator which is able todevelop a desired acceleration during increase in speed.

Another object of the present invention is to provide a cruise controlsystem employing the negative pressure type actuator which is able torestore the vehicle speed to an originally set speed in a short timeduring resume operation.

Yet another object of the present invention is to provide a cruisecontrol system which is simple in construction and is adapted to ensureas comfortable driving as possible even on an ascent while minimizingfuel consumption.

Briefly stated, the cruise control system of the present invention isequipped with an overdrive controller which releases the overdrive atthe time of operating an increase set switch and which resumes theoverdrive at the time of releasing the operation of the increase setswitch, or an overdrive controller which releases the overdrive at thetime of operating a resume switch when the vehicle speed at that time issufficiently lower than a set speed, and which resumes the overdrivewhen the vehicle speed has returned substantially to the set speed. Bythe operation of such an overdrive controller, during an increase set orresume operation the engine speed is increased to lower the intakemanifold absolute pressure, thus enhancing the actuator generatingpower. Furthermore, the cruise control system, the present invention,which is adapted to prevent reduction of the vehicle speed whileascending a slope by releasing and resuming the overdrive, is equippedwith a timer which is reset when the vehicle speed has lowered and isset when the vehicle speed has returned to a set speed so that theresumption of the overdrive is deferred by the set time of the timereven when the vehicle speed has been restored to the set speed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating the principal part of anembodiment of the present invention;

FIG. 2 is a diagram explanatory of the operation of the embodiment shownin FIG. 1;

FIG. 3 is a diagram schematically showing the outline of theconstruction of a negative pressure type actuator;

FIG. 4 is a block diagram illustrating the principal part of anotherembodiment of the present invention; and

FIG. 5 is a block diagram illustrating the principal part of still afurther embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 1, an embodiment of the present invention will bedescribed. In FIG. 1, reference numeral 100 indicates an F-V converter;101 designates a comparator; 102 identifies an analog memory circuit;103 denotes an analog switch; 104 represents a phase lead compensationcircuit; 105 shows an OR circuit; 106 and 107 refer to drivers; 108signifies a control valve solenoid in a negative type actuator; 109indicates an overdrive cut solenoid; 110 designates an increase setswitch; 111 identifies an overdrive controller; and a to c denotesignals occurring at respective parts of the cruise control system. Avehicle speed signal is converted by the F-V converter 100 into avoltage a corresponding to a vehicle speed, which voltage is applied toone input of the comparator 101 for comparison with the output voltage bfrom the analog memory circuit 102. In the analog memory circuit 102 isstored, as a set vehicle speed, a mean voltage corresponding to thevehicle speed during the ON state of the analog switch 103 ganged with aset switch (not shown); therefore, the output from the comparator 101 isrepresentative of an error signal between the current vehicle speed anda set one desired for constant speed driving. This error signal isapplied as a control signal c to the control valve solenoid 108 of thenegative pressure type actuator via the phase lead compensation circuit104 for compensating for hysteresis characteristics of the controlsystem and via the OR circuit 105 and the driver 106.

The output signal a from the F-V converter 100 becomes such, forinstance, as indicated by the solid line 200 in FIG. 2(A) when thecurrent vehicle speed is a little higher than the set vehicle speed, andbecomes such as indicated by the broken line 201 in FIG. 2(A) when thecurrent vehicle speed is a little lower than the set one. In eithercase, the output from the F-V converter 100 becomes a DC voltagecontaining some ripples. The control signal c for the control valve,obtained by comparing the output voltage from the F-V converter 100 withthe voltage b corresponding to the set vehicle speed indicated by thestraight line 202 in FIG. 2(A), is turned ON and OFF at a ripplefrequency as shown in FIGS. 2(B) and (C). The control valve solenoid 108in the negative pressure type actuator is driven by such a signal. FIG.3 which schematicallv indicates the construction of the negativepressure type actuator. While the control valve control signal c is ON,iron pieces 300 are each attracted by the control valve solenoid 108against a spring 301 to close an air intake valve 302 and to open anintake manifold absolute pressure valve 303, reducing pressure in theactuator. During the OFF period of the control valve control signal c,the iron pieces 300 are pulled back by the springs 301 to open theintake valve 302 and close the intake manifold absolute pressure valve303, increasing pressure in the actuator. Over a period of operation,the negative pressure in the actuator is determined by the duty ratio ofthe control signal c so that, by an actuator generating power based onthe negative pressure, an accelerator link is driven via a diaphragm304, performing constant speed drive control. In FIG. 3, referencenumeral 305 indicates a fulcrum; and 306 designates release valve coilsprovided for safety.

With reference to FIG. 1, cruise control system of this embodiment isarranged so that the output from the increase set switch 110 is appliedvia the OR circuit 105 and the driver 106 to the control valve solenoid108 as in the prior art. Furthermore, the overdrive controller 111 isprovided for releasing and resuming overdrive in accordance with thestate of an input electric signal. The output from the increase setswitch 110 is provided via the driver 107 to the overdrive cut solenoid109. Accordingly, upon depression of the increase set switch 110, acurrent flows to the control valve solenoid 108 to increase the actuatorgenerating power and, at the same time, a current is also applied to theoverdrive cut solenoid 109 in the overdrive controller 111 to releasethe overdrive to effect a gear change, increasing the engine speed tofurther enhance the actuator generating power. Accordingly, accelerationduring speed increase becomes larger than in the past, creating apleasant feeling.

Upon release of the increase set switch 110, the current supply to theoverdrive controller 111 is cut off and overdrive is resumed and,further, the analog switch 103 operates to store a newly set vehiclespeed in the analog memory 102, performing constant speed drive at theset vehicle speed thereafter.

The overdrive controller 111 may be of any arrangement if it is able torelease and resume the overdrive in accordance with the state of theinput electric signal. It is possible to adopt, for instance, such anoverdrive controller employed in an automatic transmission vehicle whicheffects a gear change from overdrive to third gear by means of anelectromagnetic clutch. Of course, the present invention is alsoapplicable to a manual transmission vehicle.

As described above, the cruise control system of this embodiment, whichhas the increase set function, is equipped with the overdrive controllerwhich releases overdrive when operating the increase set switch andresumes overdrive when releasing the operation of the increase setswitch. Since the actuator generating power during the increase invehicle speed is made larger than in the prior art, sufficientacceleration to satisfy the driver's requirement can be obtained, givingthe driver a sporty drive.

FIG. 4 illustrates in block form the principal part of anotherembodiment of the present invention. Reference numeral 400 indicates aF-V converter; 401 designates an adder; 402 and 403 identifycomparators; 404 denotes an analog memory circuit; 405 represents ananalog switch; 406 shows a phase lead compensation circuit; 407 and 408refer to AND circuits; 409 to 411 signify drivers; 412 indicates anegative pressure type actuator; 413 and 414 designate its control valvesolenoid and release valve solenoid respectively; 415 identifies a setswitch; 416 denotes a resume switch; 417 represents a self-sustainingcircuit; 418 shows a parking switch; 419 refers to a clutch switch; 420signifies a cancel signal generator; 422 and 423 indicate flip-flops;424 designates an overdrive start and stop unit; 425 identifies itsoverdrive cut solenoid; 426 and 427 denote reference voltages; 428represents an overdrive controller; and d to h show signals occurring atrespective parts.

In FIG. 4, a vehicle speed signal is converted by the F-V converter 400into the voltage d corresponding to the vehicle speed and applied to theone input of the adder 401, wherein it is added to the output voltage efrom the analog memory circuit 404 in the polarity shown. The analogmemory circuit 404 has stored therein, as the set vehicle speed, a meanvoltage corresponding to the vehicle speed during the ON state of theanalog switch 405 ganged with the set switch 415. Accordingly, theoutput from the adder 401 is representative of an error signal f betweenthe current vehicle speed and the set vehicle speed desired for constantspeed drive. By the closure of the set switch 415, the self-sustainingcircuit 417 is set and, by its output g, the AND circuit 407 is openedand a current is provided to the release valve solenoid 414 to make thenegative pressure type actuator 412 operable. The abovesaid error signalf is applied as a control signal h to the control valve solenoid 413 viathe phase lead compensation circuit 406 for compensating hysteresischaracteristics of the control system, the AND circuit 407 and thedriver 409, starting the constant speed drive operation.

The output signal d from the F-V converter 400 becomes such, forexample, as indicated by the solid line 200 in FIG. 2(A) when thecurrent vehicle speed is a little higher than the set vehicle speed, andbecomes such as indicated by the broken line 201 in FIG. 2(A) when thecurrent vehicle speed is a little lower than the set vehicle speed. Ineither case, the output from the F-V converter 400 becomes a DC voltagecontaining some ripples. The control signal h for the control valve,obtained by comparing the output voltage from the F-V converter 400 withthe voltage corresponding to the set vehicle speed indicated by thestraight line 202 in FIG. 2(A), is turned ON and OFF at the ripplefrequency as shown in FIGS. 2(B) and (C). Accordingly, as is the casewith the foregoing embodiment, the negative pressure in the actuator isdetermined by the duty ratio of the control signal h and, by theactuator generating power based on this negative pressure, theaccelerator link is driven via the diaphragm 304, performing theconstant speed drive control.

The cancel signal generator 421 in FIG. 4 is to generate a cancel signalto reset the self-sustaining circuit 417, for instance, when a brakepedal is stepped on, a clutch is cut off or a parking brake operates.Upon resetting of the self-sustaining circuit 417, the AND circuit 407is closed and the current supply to the release valve 414 is cut off,forcibly making the negative pressure type actuator inoperative togradually decrease the vehicle speed. The resume function is to returnthe vehicle speed to the original set speed without calling for adriver's operation of the accelerator pedal in such a case. To performthis, the present embodiment is designed so that the self-sustainingcircuit 417 is set by the output from the resume switch 416 as in theprior art. At the same time, the overdrive controller 428 is providedwhich releases the overdrive at the time of operating the resume switchwhen it is decided that the vehicle speed at that time is sufficientlylower than the set speed, and resumes the overdrive when the vehiclespeed has returned substantially to the set speed.

That is to say, in the first comparator 402, the output voltage f fromthe adder 401 is compared with the first reference voltage 426 set to avalue corresponding to about 10 Km/h, by which it is decided whether thecurrent vehicle speed is about 10 Km/h lower than the set speed, and ifso, the first flip-flop 422 is set. The second flip-flop 423, which isset at the time of operating the resume switch 416, is provided fordeciding whether the resume operation is being carried out. By the ANDoutput of the set outputs of the flip-flops 422 and 423, the overdrivecut solenoid 425 in the overdrive start and stop unit 424 is excited.The overdrive start and stop unit 424 is to release and resume theoverdrive in accordance with the state of the input electric signal. Theunit 424 may be, for instance, of such an arrangement as is employed inan automatic transmission vehicle which performs a gear change from theoverdrive to third gear through an electromagnetic cluth. It is a matterof course that other arrangements, for example, used in manualtransmission vehicle can also be used.

With such an arrangement as described above, when the vehicle speed atthe time of operating the the resume switch 416 is about 10 Km/h lowerthan the set speed, the overdrive is released substantially concurrentlywith the operation of the resume switch to effect a gear change, bywhich the engine speed is increased and the actuator generating power ismade larger than in the past. As a result of this, acceleration duringthe resume operation increases, permitting the vehicle speed to returnto the set speed in a short time.

In the second comparator 403, the output voltage from the adder 401 iscompared with the second reference voltage 427 set to a valuecorresponding to about 3 Km/h, and the flip-flops 422 and 423 are resetby the output from the comparator 403 when the vehicle speed has beenrestored substantially to the set speed. Accordingly, when the vehiclespeed has returned almost to the set speed, the overdrive is switchedagain.

It is also possible to make such an arrangement that, for example, whenthe vehicle speed has lowered below 40 Km/h, the content of the analogmemory circuit 404 is cleared, thereby to inhibit the resume operationwhen the vehicle speed is below the abovesaid value.

As described above, according to this embodiment, the cruise controlsystem having the resume function is provided with the overdrivecontroller which releases the overdrive at the time of operating theresume switch when the vehicle speed at that time is sufficiently lowerthan the set speed, and resumes the overdrive when the vehicle speed hasbeen restored substantially to the set speed. Since the actuatorgenerating power during the resume operation can be enhanced as comparedwith that in the prior art, the original set vehicle speed can berestored in a short time, giving the driver a sporty drive.

FIG. 5 illustrates in block form the principal part of anotherembodiment of the present invention. Reference numeral 500 indicates anF-V converter; 501 designates an adder; 502 identifies an analog memorycircuit; 503 denotes an analog switch; 504 represents a phase leadcompensation circuit; 505 and 506 show amplifiers; 507 refers to anegative pressure type actuator; 508 signifies its control valvesolenoid; 509 and 510 indicate comparators; 511 and 512 designate theirreference voltages; 513 identifies a flip-flop; 514 denotes a timer; 515represents an inverter; 516 shows an overdrive start and stop unit; 517refers to its overdrive cut solenoid; and i to l signify signalsoccurring at respective parts of the cruise control system.

In FIG. 5, a vehicle speed signal is converted by the F-V converter 500into a voltage i corresponding to the vehicle speed and is applied tothe one input of the adder 501, wherein it is added to the outputvoltage j from the analog memory circuit 502 in the polarity shown. Theanalog memory circuit 502 has stored therein a mean voltagecorresponding to the vehicle speed during the ON state of the analogswitch 503 ganged with a set switch (not shown). According, the outputfrom the adder 501 is indicative of a voltage corresponding to adifference between the current vehicle speed and a set speed desired forconstant speed drive, i. e. a voltage k corresponding to an error speed.The voltage k corresponding to the error speed is provided as a controlsignal l to the control valve solenoid 508 of the negative pressure typeactuator 507 via the phase lead compensation circuit 504 forcompensating hysteresis characteristics of the control system and viathe amplifier 505, carrying out a predetermined constant speed drivecontrol. That is, as is well known in the art, the intake manifoldabsolute pressure is introduced into the actuator in accordance with theduty ratio of the control signal l and, by the actuator generating powerbased on this pressure, the accelerator link is driven, performingcontrol to bring the vehicle speed to the set value. Incidentally, it isa matter of course that the actuator may also be an actuator employingthe motor system mentioned above.

In the first comparator 509, the error speed corresponding voltage kfrom the adder 501 is compared with the first reference voltage 511 setto a value corresponding to a speed predetermined as a reduced speed atwhich the overdrive should be released, for instance, about 7 Km/h. Bythis comparison, it is detected whether the current vehicle speed hasbecome lower than the set speed by approximately 7 Km/h, and if so, theflip-flop 513 is set. The set output from the flip-flop 513 is appliedvia the amplifier 506 to the overdrive cut solenoid 517 of the overdrivestart and stop unit 516. The overdrive start and stop unit 516 is torelease and resume the overdrive in accordance with the state of theinput signal as in the case of the automatic transmission vehicle whichcarries out a gear change from the overdrive to third gear through anelectromagnetic clutch, for instance. Upon setting of the flip-flop 513,the overdrive cut solenoid 517 is turned ON to release the overdrive.Accordingly, the vehicle speed that was reduced while ascending a slopeis gradually increased.

When the vehicle speed has increased to almost reach the set speed, itis detected by the second comparator 510 which compares the secondreference voltage 512 set to a value corresponding to, for instance,about 3 Km/h, with the error speed corresponding voltage k, and thedetected output is provided to the timer 514 to set it. The timer 514 isset so that it yields an output "1" at a preset time of approximately 15seconds after its setting to hereby reset the flip-flop 513. Therefore,even when the vehicle speed has restored substantially to the set speed,the overdrive is not immediately resumed unlike in the prior art butinstead the flip-flop 513 is reset only after the lapse of the presettime of the timer 514, by which the overdrive cut solenoid 517 is turnedOFF, permitting resumption of the overdrive. Though differing a littlewith the grodients of road, if the preset time of the timer 514 shouldbe selected to be about 15 seconds, one cycle of a change in the vehiclespeed including a vehicle speed decreasing or increasing time wouldbecome longer than approximately 30 seconds and an unpleasant drive byfrequent speed changes could be avoided. Moreover, since the overdriveis not released during driving at all times, fuel expense can also becut down. Incidentally, the timer 514 is reset by the output from theinverter 515 when the vehicle speed is about 3 Km/h lower than the setspeed.

As described above, according to this embodiment, the cruise controlsystem, which prevents a slow down of the speed while hill climbing byrelease and resumption of the overdrive, is provided with a timer whichis reset when the vehicle speed has lowered and is set when the vehiclespeed has been restored almost to the set speed, and the resumption ofthe overdrive is retarded by the preset time of the timer. Accordingly,a comfortable drive during hill climb can be ensured with a simplearrangement. Furthermore, since the overdrive is not released duringdriving at all times, the cost of fuel is not so much increased.

The present invention is not limited specifically to the foregoingembodiments, and other variations and modifications may be effected. Itis a matter of course that the present invention is applicable not onlyto the auto transmission vehicle but also to a manual transmissionvehicle. It is also possible to store the set vehicle speed digitallyand to perform the functions of the phase lead compensation circuit, thecomparators and the timer through utilization of the arithmetic functionof a microprocessor.

It will be apparent that many modifications and variations may beeffected without departing from the scope of the novel concepts of thepresent invention.

What is claimed is:
 1. A cruise control system for controlling the speedof a vehicle, comprisingfirst means for setting a desired speed for saidvehicle, for comparing the actual speed of said vehicle with saiddesired speed, and for providing an output corresponding to thedifference therebetween, a negative pressure type actuator whichcontrols an accelerator of the vehicle according to said output of saidfirst means, automatic gearshift means for providing an automaticgearshift function from a high gear to a lower gear of said vehicle andback and, second means for operating said automatic gearshift means, forautomatically shifting from said high gear into said lower gear when theactual speed of said vehicle is at least a first predetermined amountless than said desired speed, and for shifting back to said high gear ata predetermined time with respect to when the actual speed comes withina second predetermined amount of said desired speed, said firstpredetermined amount being larger than said second predetermined amount.2. The system of claim 1, said second means includingmeans for supplyinga first reference voltage corresponding to said first predeterminedamount, a first comparator for comparing said output of said first meanswith said first reference voltage, and for providing an output dependingon which is larger, means for supplying a second reference voltagecorresponding to said second predetermined amount, a second comparatorfor comparing said output of said first means with said second referencevoltage, and for providing an output depending on which is larger, atimer that is set by a change in said output of said second comparatorcorresponding to said actual vehicle speed coming within said secondpredetermined amount of said desired speed, and reset by the oppositechange, to provide a timer output at a predetermined time after thetimer is set, and a flip-flop that is set by a change in said output ofsaid first comparator corresponding to said actual speed becoming lessthan said desired speed by said first predetermined amount, and reset bysaid timer output, to provide a flip-flop output to control saidshifting between said high gear and lower gear, wherein said shiftingfrom said lower gear to said higher gear occurs at said predeterminedtime after the actual speed be comes within said second predeterminedamount of said desired speed.
 3. The system of claim 2, said desiredspeed set in said first means being the actual speed of said vehicle atthe time that is stored in said first means.